The present invention relates to the field of medical technology, particularly to an apparatus to be implanted in an eyeball for the treatment of glaucoma.
Glaucoma is one of the leading causes of blindness in the United States. It is estimated that two to three million people in the United States have some degree of visual loss resulting from glaucoma. While glaucoma is a medical condition which can be caused by several factors, excessive intraocular pressure is a major risk factor for developing glaucoma. Over time, excessive intraocular pressure can cause damage to the optic nerve resulting in gradual loss of vision and, in some cases, blindness. Excessive intraocular pressure is caused by an increase in the resistance to outflow of fluid, called aqueous humor, in the anterior chamber of the eyeball, which can be caused by a number of different factors including injury, the aging process, reaction to medication (such as corticosteroids), structural abnormalities within the eyeball, and a genetic predisposition.
Aqueous humor is a clear, watery fluid which is constantly circulated within the anterior chamber of the eyeball. It serves to nourish the cornea and lens and to provide the intraocular pressure necessary to maintain the shape of the eyeball. Aqueous humor exits the anterior chamber through a network of spongy tissue called the trabecular meshwork, which is located in the intersecting space (the angle) between the iris and the cornea. Increased intraocular pressure results when aqueous humor cannot drain properly or at an appropriate rate through the trabecular meshwork or other outflow pathways. The only proven treatment for glaucoma is to reduce intraocular pressure.
Increased intraocular pressure can in some cases be treated with appropriate medication. These medications are usually administered through pills or eye drops and work to either decrease the rate at which aqueous humor flows into the eyeball, or to increase the rate at which aqueous humor drains from the eyeball. However, as with any medication, patients experience different levels of response to the medication, and the side effects of some medications can become intolerable in certain individuals.
Surgical procedures are also employed to treat glaucoma. Certain procedures are referred to as “filtration” procedures, since the end goal of these particular surgical procedures is to increase the outflow of aqueous humor from the anterior chamber, thereby reducing intraocular pressure. Procedures focused on increasing the outflow of aqueous humor from the anterior chamber of the eyeball are theoretically more beneficial than those designed to decrease the production of aqueous humor, as over 95% of glaucomatous disease is a consequence of increased outflow resistance or reduced outflow rate rather than increased aqueous humor production or increased venous pressure distal to the outflow channels. Full thickness filtration surgical procedures involve the creation of an alternate route for the aqueous humor to flow from the anterior chamber of the eyeball into the subconjuctival space with the formation of a bleb—an area of limbal (anterior) filtration—which contains the aqueous humor. Guarded filtration surgical procedures, such as a trabeculectomy, involve the surgical creation of an opening which is covered by partial thickness sclera, from the anterior chamber into the subconjunctival space, thereby resulting in increased aqueous humor flow out of the anterior chamber. Unfortunately, the failure rate of filtration procedures is unacceptably high. In addition, postoperative intraocular pressure is almost always unstable and unpredictable. Initial overdrainage can lead to abnormally low intraocular pressure, known as hypotony, which can cause the eyeball to malfunction and delay the patient's postoperative recovery. Also, scarring or excessive resistance may occur in the subconjunctival, episcleral, or scleral regions (i.e., the sclerostomy site or surgical opening into the anterior chamber), thereby restricting the drainage.
Surgical procedures have also been used to reduce the amount of aqueous humor production within the eyeball. Ciliodestructive surgery, also known as cyclocryotherapy or cyclophotocoagulation, involves the use of either cryotherapy or a laser on the surface of the eyeball to reduce the production of aqueous humor. However, this procedure can cause a decrease in vision, and is usually used as a last resort when other procedures have failed.
Another method of treating intraocular pressure involves the use of drainage devices implanted within the anterior chamber as a means to drain aqueous humor while maintaining proper intraocular pressure. These devices typically incorporate a tube situated within the anterior chamber which drains aqueous humor from the anterior chamber into a surgically created posterior reservoir, called a fibrous capsule, formed around the scleral explant of the device. The aqueous humor which drains into the fibrous capsule is eventually resorbed by the body. Some of these drainage devices employ valve mechanisms to provide resistance to aqueous humor outflow. These valves have been shown to be unpredictable in their performance, resulting in excessive outflow of aqueous humor and possible hypotony. The valves can also become clogged and cease to function altogether, which results in an increase in intraocular pressure. Also, the fibrous capsule can become scarred or can develop excessive resistance, resulting in failure and a need for surgical revision. In addition, the insertion process for properly implanting these drainage devices within the eyeball can often be very complex and time consuming, increasing the duration of the surgical procedure itself and the postoperative recovery period for the patient.
Certain drainage devices have been developed to reduce intraocular pressure by draining aqueous humor from the anterior chamber to the external surface of the eyeball, as shown by U.S. Pat. No. 5,346,464 to Camras (see also U.S. Pat. Nos. 6,595,945 to Brown, 4,886,488 to White, 5,743,868 to Brown and 5,807,302 to Wandel). These drainage devices have the added benefit of not requiring the creation of a bleb or fibrous capsule for drainage. Therefore, the surgical outcome is not influenced by the possibility of subconjunctival scarring. The devices described in the prior art have not eliminated potential problems such as difficulty of proper insertion, failure of the device, unpredictable postoperative intraocular pressure without a means to compensate or adjust the device for optimal results, and/or extended postoperative recovery time. Additionally, some of these devices do not adequately guard against the potential for infection by entry of microorganisms either through or around the device.
There exists a need in the art for a means to treat glaucoma which is predictable, which allows for the post-surgical adjustment of intraocular pressure, which results in long-term efficacy, which limits the risk of infection, which is comfortable for the patient, and which can be properly inserted both quickly and easily. The present invention meets these needs.